A three-dimensional (3-D) finite element model for stress analysis of pavements with ultrathin whitetopping (UTW) under critical loading conditions was developed. The 3-D model developed was used to analyze the UTW test pavement sections at the Ellaville Weigh Station in Florida, which had less than satisfactory performance. The poorly performing UTW sections at the Ellaville Weigh Station were found to have relatively higher maximum computed stresses under critical loading conditions, which appeared to explain their poor performance and high percentages of cracked slabs. The 3-D model developed was also used to perform a parametric analysis to determine the effects of asphalt thickness, asphalt modulus, concrete thickness, concrete modulus, base stiffness, subgrade stiffness, slab dimension, temperature differential in the concrete, and applied load on the maximum stresses in UTW pavements under typical Florida conditions.
As part of a study sponsored by NCHRP, research was conducted to evaluate the variability of concrete materials data in the Long-Term Pavement Performance (LTPP) program. The following materials-related data were studied: ( a) compressive strength, ( b) flexural strength, ( c) split tensile strength, and ( d) modulus of elasticity. The variability was determined in terms of the standard deviation and coefficient of variability. The strength and stiffness data used came from the General Pavement Study (GPS) as well as the Specific Pavement Study (SPS) test sections. The analysis of data indicates that, in general, the LTPP program GPS test sections as well as the LTPP program SPS test sections exhibit characteristics of well-controlled construction projects with respect to the strength- and stiffness-related properties of concrete. The results of the analysis indicate that on well-controlled concrete pavement construction projects it would not be unreasonable to produce concrete that has a coefficient of variation of 15% or less for compressive strength, flexural strength, split tensile strength, and the modulus of elasticity. The findings from the analysis can be used to refine statistics-based quality assurance/quality control procedures for concrete acceptance and to define the measures of variability to be used in mechanistically based concrete design procedures.
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